Summary
Summary Unit 2 - Cells Active Transport
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Unit 2 - Cells Active Transport
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Active TransportActive Transport is the movement of molecules against a concentration gradient from an area of
low to high concentration. This requires energy and carrier proteins.
Carrier proteins are involved as a molecule attaches itself to a carrier protein causing it to
change shape so the molecule can move across the membrane.
Energy is required to make the carrier protein change shape so the molecules or ions can be
transfered across the cell membrane.
1. The molecule or ion binds to the carrier protein in the plasma membrane at the receptor
site.
2. The ATP binds to the protein on the other side causing it to split by hydrolysis into ADP
and Pi, releasing energy.
3. The protein changes shape and opens on the other side of the membrane.
4. The molecule or ion is released on the other side of the membrane.
5. ATP is reformed and the protein reverts to its original state.
Similar to facilitated diffusion but there are differences:
Active transport moves solutes from a low to high concentration while in facilitated
diffusion it is from a high to low concentration.
Active transport requires energy from ATP which is produced by respiration. ATP
undergoes a hydrolysis reaction splitting it into ADP and Pi. This releases energy.
Facilitated diffusion doesn't require energy.
Active transport doesn't use channel proteins only carrier - while facilitated uses both.
Examples of active transport.
- absorption of amino acids from the gut into the blood -mineral ions entering the roots of a
plant -exchange of sodium and potassium ions (nerve impulses) -endocytosis -exocytosis
(phagocytosis)
Factors that affect active transport:
Speed of carrier proteins
Number of carrier proteins
Rate of respiration
Anything that affects respiration - enzymes needed for respiration
Anything that affects enzyme activity
Amount of ATP available
Increased concentration gradient
Co-transporters are a type of carrier protein which bind to two molecules at once. The
concentration gradient of one molecule is used to move the other molecule against the
concentration gradient.
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